1. Field of the Invention
The present invention relates generally to reducing power consumption in a portable device capable of receiving Global Navigation Satellite System (GNSS) signals, and more particularly, to minimizing signal acquisition time and the number of required tracking channels in a portable device having a GNSS receiver using information regarding the portable device's current location.
2. Description of the Related Art
Satellite navigational systems provide positional and timing information to earth-bound receivers. Each system has its own constellation of satellites orbiting the Earth, and, in order to calculate its position, a receiver on Earth uses the satellites “in view” (i.e., in the sky above) from that system's constellation. Global Navigational Satellite System (GNSS) is often used as the generic term for such a system, even though such navigational satellite systems include regional and augmented systems—i.e., systems that are not truly “global.” The term “GNSS,” as used herein, covers any type of navigational satellite system, global, regional, augmented or otherwise, unless expressly indicated otherwise.
The number of GNSS systems, both planned and presently operational, is growing. The widely-known, widely-used, and truly global Global Positioning System (GPS) of the United States has been joined by one other global system, Russia's GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS), and is presently being joined by Europe's Galileo and China's BeiDou (also known, in its second generation, as COMPASS) systems—each of which has, or will have, its own constellation of satellites orbiting the globe. Regional systems (those that are not global, but intended to cover only a certain region of the globe) include Japan's Quasi-Zenith Satellite System (QZSS) and the Indian Regional Navigational Satellite System (IRNSS) currently being developed. Augmented systems are normally regional as well, and “augment” existing GNSS systems with, e.g., messages from ground-based stations and/or additional navigational aids. These include the Wide Area Augmentation System (WAAS), European Geostationary Navigation Overlay Service (EGNOS), Multi-functional Satellite Augmentation System (MSAS), and GPS Aided Geo Augmented Navigation (GAGAN). Regional GNSS systems, such as QZSS, can also operate as augmented systems.
Moreover, GNSS capabilities are no longer limited to any particular type of system or device. A GNSS receiver may be implemented in a mobile terminal, a tablet computer, a camera, a portable music player, and a myriad of other portable and/or mobile personal consumer devices, as well as integrated into larger devices and/or systems, such as the electronics of a vehicle. The term “GNSS receiver” as used herein, covers any such implementation of GNSS capabilities in a device or system.
Broadly speaking, the reception/processing of GNSS signals involves three phases: acquisition, tracking, and positional calculation (or “navigation solution”). Acquisition is the acquiring or identifying of the current satellites in view (SVs), which means satellites that are “visible” overhead, i.e., the satellites from which the GNSS receiver can receive signals. Obviously, in any “global” GNSS constellation of satellites, roughly half of the satellites are orbiting on the other side of the planet at any time. Acquisition uses one or more of satellite almanac information, the GNSS receiver's last positional calculation, assistive information concerning the local region received by terrestrial transmission, signal processing (specifically, finding satellite signals by correlating known signal patterns), and other means well-known by those of ordinary skill in the art, in order to acquire the current SVs. Acquisition can be understood as “finding” the SVs, tracking is the fine tuning of the signals received from the acquired SVs and the keeping track of the acquired SVs over time. Once acquired and adequately tracked, the SV's signals are processed to extract the navigational, positional, timing, and other data transmitted in each SV's signal, and the data from all the SV's being tracked is then used to calculate the GNSS receiver's position. Of course, there are further complexities to the actual reception and processing of GNSS signals, such as various loops feeding back information between these phases for further correction and adjustment of data, as is known to one of ordinary skill in the art.
When a GNSS receiver is implemented in a portable and/or mobile device which relies upon one or more batteries for power, the components used for GNSS signal reception, signal processing, and positional calculation use a substantial amount of the power budget when in use. When the GNSS capability is being used for continuous updating of positional information, such as when navigating a route in a moving vehicle or while walking in unfamiliar terrain, it is a particularly large drain on the one or more batteries.
More specifically, when in an environment where the “view” of the GNSS receiver is completely blocked for large regions of the sky, large amounts of battery power are wasted both in attempting to acquire SVs which can never be acquired and tracking SVs which can no longer be tracked.
The waste is not trivial, as every milliamp (mA) decreases the battery life of a portable device. Such battery power consumption spent on tasks which, by definition, can never succeed is a significant waste. Thus, there is a need for a system, method, and/or apparatus to reduce the power consumed in acquiring and/or tracking SVs blocked by local environmental conditions from a GNSS receiver in a portable device powered by one or more batteries.